Mobile communication apparatuses connectable to a wireless local area network (LAN) are used today. Such a mobile communication apparatus searches for (scans for), for example, an available nearby access point (base station) from among access points with air interfaces scattered over the wireless LAN. When a desired access point is detected, the mobile communication apparatus connects to the detected access point to perform communication.
The frequency band available for the wireless LAN includes the 2.4 GHz band and the 5 GHz band. In the 2.4 GHz band, 13 channels are defined, namely, channels 1 to 13. In the 5 GHz band, 19 channels are defined, namely, channels 36, 40, . . . , and 64, and channels 100, 104, . . . , and 140. In the case of using the 2.4 GHz band, the access point selects one or more channels in the 2.4 GHz band. In the case of using the 5 GHz band, the access point selects one or more channels in the 5 GHz band. There are cases in which a single access point uses both the 2.4 GHz band and the 5 GHz band.
When the mobile communication apparatus is not connected to any access point, the mobile communication apparatus searches for an access point by determining for each of the channels of the 2.4 GHz band and the 5 GHz band whether a signal in a predetermined format is received, for example. If an available access point is detected, the mobile communication apparatus performs connection processing to start communication using a channel of the 2.4 GHz band or the 5 GHz band on which the access point is detected.
There has been proposed a method that performs multiple iterations of scan. According to this scanning method, a radio communication apparatus selects passive scan or active scan for each scan, in accordance with the area where the radio communication apparatus is located. In passive scan, the radio communication apparatus detects a beacon that is periodically broadcasted by an access point. In active scan, the radio communication apparatus transmits a probe request, and detects a response to the probe request.
There has also been proposed an access point that selectively uses the 2.4 GHz band and the 5 GHz band. This access point causes a radio communication apparatus performing highly real-time communication to connect to the 5 GHz band where there is less interference than in the 2.4 GHz band, and causes another radio communication apparatus to connect to the 2.4 GHz band. The access point may cause a radio communication apparatus to perform “roaming” to move from the 5 GHz band to the 2.4 GHz band.
In the wireless LAN, the 5 GHz band has an advantage over the 2.4 GHz band. For example, although adjacent bands in the 2.4 GHz band overlap in the frequency domain, adjacent bands in the 5 GHz band do not overlap in the frequency domain. Accordingly, the 5 GHz band has less interference between channels. Further, the frequencies in the 5 GHz band have less conflict with electrical products, such as microwave ovens, and communication apparatuses of other communication systems. Further, according to some communication standards for wireless LAN, it is possible to realize faster radio communication by using the 5 GHz band than by using only the 2.4 GHz band.
See, for example, International Publication Pamphlets No. WO2008/008987, and No. WO2011/161951.
Radio areas of a plurality of frequency bands (for example, the 2.4 GHz band and the 5 GHz band) are sometimes formed to concentrically overlap each other. For example, in the case where one access point uses a plurality of frequency bands, radio areas of the plurality of frequency bands are formed around the access point. If a mobile communication apparatus starts a search in the vicinity of the access point, the mobile communication apparatus may connect to the access point in any of the frequency bands.
However, different frequency bands often have different sizes of radio areas. For instance, the propagation distance of a radio signal of the 2.4 GHz band is often greater than that of a radio signal of the 5 GHz band, and therefore the 2.4 GHz band often has a larger radio area than the 5 GHz band. Accordingly, in the case where a mobile communication apparatus moves toward an access point from a distant location, the mobile communication apparatus is likely to connect to the access point in a specific frequency band first (for example, a band of lower frequencies such as the 2.4 GHz band or the like). Then, if the connection is maintained as long as the radio conditions of the connected frequency band are good, the mobile communication apparatus will not have an opportunity to reconnect to the access point in another frequency band (for example, a band of higher frequencies such as the 5 GHz band or the like). Thus, even when a plurality of frequency bands are available, there is a variation between the frequency bands in how often the frequency bands are used.
One way to address this issue is to, even after a connection to an access point is established in a frequency band, continuously search for an access point in another frequency band, and perform reconnection when the radio conditions of the other frequency band are improved. However, continuous search in another frequency band imposes a high load on the mobile communication apparatus. For example, in the case where a connection is established in the 2.4 GHz band, communication in the 2.4 GHz band might be temporarily suspended in order to perform a search in the 5 GHz band.